I can also heartily recommend
Grasmere Lodge, which is 90 minutes from Christchurch, up in the mountains as you approach Arthurs Pass. The scenery is stunning, service & food top notch, and the room we had was beyond fantastic (we stayed in the Riverview Cottage). ^
Included in our stay was an excellent tour of the local area on our first day, which included a very light trek to see salmon spawning and other natural sights. The next day we had a tour of the working farm (we paid an extra supplement for this), which included a sheepdog exhibition and a sheep shearing demonstration. We got to feed some of the sheep, which I found to be a highlight. Graeme, the resident nature guide, is extremely knowledgeable about both the local flora and fauna and also the workings of sheep farming. Tom, the owner and manager, is an affable guy who joins the guests for pre-dinner drinks and is himself a wealth of knowledge about other NZ luxury lodges.
All in all, highly recommended.